1. Field of the Invention
The present invention relates to an image heating apparatus suitable for use as a fixing apparatus to be mounted on an image forming apparatus, such as a copying machine and a laser beam printer (LBP), which adopts an image forming process such as an electrophotographic printing method and an electrostatic recording method.
2. Description of the Related Art
As disclosed in Japanese Patent Application Laid-Open No. H11-024492, a fixing apparatus configured to fix, onto a recording material, a toner image formed on the recording material is provided with an excessive-temperature-rise protection element (thermal fuse or thermo switch) to be activated when sensing an excessive rise in temperature (abnormal rise in temperature) of the fixing apparatus so as to interrupt power supply to a heating member (heater).
By the way, even when the fixing apparatus is brought into a state in which the temperature rises excessively, it cannot be determined whether the excessive rise in temperature is caused by a failure of a drive element (thyristor such as a triac) configured to control the power supply to the heater, or by a malfunction (an incorrect operation) of the drive element instead of the failure. Therefore, even when the fixing apparatus is brought into the state in which the temperature rises excessively due to the failure of the drive element, the mechanical drive (rotating state) of a rotary member,. such as a fixing roller, is maintained until the excessive-temperature-rise protection element interrupts the energization of the heater in a mechanical manner. When the drive element fails, there is a fear in that the power supply to the heater cannot be interrupted. In this case, when the mechanical drive is maintained, positive natural heat dissipation from the rotary member is also maintained, but heat transfer to a component (such as a pressure roller) held in contact with the rotary member is continued. Then, until the temperature reaches to the activation temperature of the protection element, the heat is accumulated in the component held in contact with the rotary member, and in another component (such as a gear) held in contact with that component. Thus, there is a fear of thermal damage to those components.
The fixing apparatus is in failure, and therefore needs to be replaced, but the thermally damaged components can no longer be reused.